However, it also uses a hammering function to create a vibrating action, causing energy to be transferred to the chuck and the bit. The vibrating action causes the bit to chip away at whatever it’s hammering against. A hammer drill exerts force in line with the bit as it hits the material being drilled, making it the tool of choice for drill­ing holes in masonry and concrete. An impact driver is somewhat similar to a hammer drill, but it increases the force being delivered perpendicular to the bit, making it the preferred tool for driving large screws and lag bolts. A hammer drill shouldn’t be confused with a rotary hammer, which uses a pis­ton, driven by a motor and gearing system, to pound a bit into mate­rial, which makes it a preferred tool among construction workers. In general, hammer drills are suit­able both for drilling and driving long and wide screws and lag bolts into wood, and for hammer drilling holes up to about 3/4″ diameter in concrete block or brick. There are also hammer drill/driver tools that provide two modes of operation: a conventional “drilling and driving mode” that you use when accuracy in hole size and depth is crucial; and a “hammering mode” that adds a pounding force to the tool for extra-hard materials. Hammer drills are available in both corded and cord­less formats.